Method and apparatus for growing crystals



Aug. 29,1967 K. WEISER ET AL METHOD AND APPARATUS FOR GROWING CRYSTALS Filed April 27, 1961 M 0& mum 1m E [L VWW W M m ATTORNEY United States Patent York Filed Apr. 27, 1961, Ser. No. 106,099 3 Claims. (Cl. 23-204) This invention relates to a method and apparatus for growing crystals. In accordance with one embodiment, this invention is particularly directed to a method and apparatus for growing crystals, such as single crystals or monocrystals, of semiconductive materials. Still more particularly, this invention relates to a method and apparatus for growing and pulling crystals of material having a relatively high vapor pressure or dissociation pressure during the crystal growing and pulling operations.

In the growing and pulling of crystals composed of materials having a relatively high vapor pressure or dissociation pressure at the crystal growing and pulling temperature, it is particularly diflicult to grow and pull such crystals since, during the lengthy (usually many hours or days) crystal growing and pulling operations the crystals tend to vaporize or dissociate, oftentimes to a very great extent so that the yield of grown crystal is very substantially reduced, even to the extent of rendering the crystal growing and pulling operations impractical.

It is an object of this invention to provide an improved method and apparatus for growing and pulling crystals.

It is another object of this invention to provide an improved method and apparatus for growing crystals of materials having a relatively high vapor pressure or dissociation pressure at the crystal growing or pulling temperature.

Still another object of this invention is to provide a method and apparatus whereby loss of crystalline material of a material possessing a relatively high vapor pressure during the crystal growing or pulling operation is substantially reduced.

Yet another object of this invention is to provide a method and apparatus for the in situ production of crystal-forming material.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing wherein there is schematically illustrated apparatus suitable for use in the practice of this invention, the drawing at the same time being illustrative of a method of this invention.

In accordance with this invention an improved method of growing crystal-forming material, such as crystalforming material having a relatively high vapor pressure or dissociation pressure during the crystal growing or pulling operation, is provided by producing said material in situ with a closed zone or chamber in the presence of or in an atmosphere containing a gaseous or vaporized component or constituent of said material maintained at the vapor pressure or dissociation pressure of said material at the temperature employed during the crystal growing or pulling operation. More particularly, in accordance with this invention, there is provided a method and apparatus for growing crystalline material, such as material having the composition AB, which comprises maintaining a body of component A within a container in a closed contacting zone, contacting component A within said zone with vaporized component B under conditions such that component A forms with vaporized component B said material AB in said container, forming a melt of resulting material AB in said container within said zone in contact with vaporized component B, introducing suitable seeding material, such as a seed crystal of material AB, into direct contact with said melt containing material AB therein, maintaining said seeding material in contact with said melt under crystal growing conditions to form on said seeding material crystalline material AB derived from said melt.

The practice of this invention is generally applicable to the growing or production of crystalline material but is particularly applicable, as indicated hereinabove, to the growing or production of crystalline material possessing a relatively high vapor pressure or dissociation pressure during the crystal growing or producing operation. Various crystalline materials may be grown and produced by following the practices of this invention but, as also indicated hereinabove, the practice of this invention is particularly applicable to the growing or production of crystalline semiconductive materials, such as gallium arsenide, indium arsenide, indium antimonide, gallium phosphide, indium phosphide and other materials such as the sulfides, tellurides, selenides of zinc, cadium, bismuth and the like. Crystalline material having the composition AB, wherein A is a lesser volatile component or element than B and wherein B reacts on contact with A to form AB, e.g. chemical compounds wherein A is an element or metal such as zinc, cadmium, bismuth, aluminum, gallium, boron and indium and B is an element or non metal such as sulfur, tellurium, selenium, nitrogen, phosphorus, arsenic and antimony, are readily produced and grown in accordance with the practices of this invention. If desired, there may be present during the crystal growing operation in the melt a minor or trace or doping amount of an element other than A or B.

Referring now to the accompanying drawing which somewhat schematically illustrates an apparatus useful in the practice of this invention, there is shown therein a closed chamber or contacting zone 10, such as a sealed quartz tube 10. Two containers, preferably made of quartz, container 11 and container 12, are disposed within quartz tube 10. Container 12 located towards one end of tube 10 is provided with a given amount of material B and container 11 located towards the other end of tube 10 is provided with a given amount of material A. Material B may suitably comprise any material which upon volatilization and subsequent contact and admixture with component A forms therewith crystal-forming material AB.

Positioned within quartz tube 10 in a substantially upright position is envelope 14, also desirably made of quartz. Seeding material or seed crystal holder 15, also preferably made of quartz, is fixed to the bottom of envelope 14 and carries at its lower end 15a seed crystal or seeding material 16, preferably of material AB. There is provided with-in quartz envelope 14 a block or cylinder 17 of soft iron or other suitable ferromagnetic material which is fixed substantially rigidly by means of member 18, such as a bar or wire, to a block 19 of soft iron or other suitable ferromagnetic material. Block 19 is of a size suitable for insertion into envelope 14 but not for rotation therein. Cleats 14a formed on the inside of the bottom of envelope 14 hold block 19 in position and prevent its rotation within envelope 14. A ring solenoid 20 provided with means, not shown, for energizing same encompasses quartz tube 10 and is disposed adjacent cylinder 17. Also a magnet 21, such as a C-shaped magnet having a north pole and a south pole encompasses quartz tube 10 and is disposed adjacent block 19. Both ring solenoid 20 and magnet 21 are supported on shelves 22a and 22b, respectively within cage 22 which is adapted for vertical movement along quartz tube 10 by means comprising internally threaded sleeve 23 which is fixed to cage 22. Sleeve 23 is threadedly engaged to screw 24 which, in turn, is adapted for rotation by motor 25 through reversible gear reducer 26 which is operatively connected to screw 24 by shaft 27 and coupling 27a.

As illustrated, container 12 is supported on top of quartz envelope 14. Container 12 is provided with a tubular central portion 12a. The tubular central portion 12a of container 12 fits over and surrounds elongated member 14a, also preferably made of quartz, fixed at one end to the top of quartz envelope 14. Elongated quartz member 14 terminates at the other end in a hook or eyelet portion 14b.

Ring solenoid 20 when energized, attracts and supports cylinder 17 and in so doing supports block 19 as Well as quartz envelope 14 carrying with it seed crystal holder 15 and container 12 positioned. atop quartz envelope 14 or otherwise suitably positioned within tube 10. Magnet 21 is mounted on gear platform or hearing 28 which is adapted for rotation. Gear platform 28 is meshed with and operatively connected to driving gear 29 which in turn is operatively connected to and meshed with axially elongated gear or pinion 31. Gear 31 is fixed to shaft 32 for rotation therewith and shaft 32 in turn is coupled via coupling 34a to shaft 34 which is adapted for rotation by motor 35 through reversible gear reducer 36. Block 19 within envelope 14 is positioned in line with poles N and S of magnet 21. Accordingly, as magnet 21 is caused to rotate about quartz envelope 14, block 19 is also caused to rotate in alignment with the N-S poles of magnet 21. Since block 19 is rigidly fastened to cylinder 17 via member 18 and since block 19 cannot rotate within envelope 14, quartz envelope 14 is caused to rotate carrying with it during rotation seed crystal holder 15.

Container 12 may rotate with or may remain stationary with respect to quartz envelope 14 depending upon the frictional forces involved between their contacting surfaces. Binding of quartz envelope 14 against the interior surface of quartz tube tends to be obviated by the combination of elongated member 14b of quartz envelope 14 and central tubular member 12a of container 12. Tubular member 12a tends to act as a sleeve bearing and guide to maintain quartz envelope 14 and seed crystal holder disposed substantially concentrically within tube 10. Vertical up or down movement of quartz envelope 14 within tube 10 is effected by rotation of screw 24, causing cage 22 and solenoid to move upwardly or downwardly along tube 10 and moving with it cylinder 17, and therefore envelope 14, cylinder 17 following the vertical movement of solenoid 20.

In the operation of the device illustrated in the drawing for the preparation of crystalline material in accordance with the practices of this invention, there is introduced into containers 11 and 12 proper amounts of materials A and B, respectively. A given amount of A is introduced depending on the amount of crystal desired to be produced and the physical dimension of the apparatus. The amount of B is immaterial as long as it is enough to react with the amount of A and to fill the vapor space within tube 10 with vapor of B at the desired pressure. The interior of tube 10 may be pressurized with an inert gas, such as helium or nitrogen, or even, if suitable, with air, or tube 10 may be filled with an inert gas or air with substantially no pressure differential between the interior of tube 10 and the ambient atmosphere outside of tube 10. Further, if desired, tube 10 may be substantially completely evacuated, such as to an absolute pressure therein in the range 0.000001 to 40 mm. Hg, more or less, the interior of tube 10 at such pressure being occupied with air or with a suitable inert gas. After the aforesaid initial preparation tube 10 is sealed, such as by heat sealing at 10a thereof.

Following the aforesaid preparation of tube 10 and the introduction of components A and B into containers 11 and 12, respectively, solenoid 20 is energized and cage 22 lifted toward the upper end of tube 10. As cage 22 and energized solenoid 20 are moved upwardly solenoid 20 attracts cylinder 17 positioned within envelope 14 with the result that as solenoid 20 is moved upwardly envelope 14 carrying with it seed crystal holder 15 are also lifted and moved along therewith. As a result seed crystal holder 15 is lifted away from container 11.

Material B is heated within container 12 to vaporize material B therefrom by placing the assembly illustrated in the drawing in a suitable furnace or by other suitable means for applying heat to material B in container 12. Also, material A is heated within container 11 by suitable means, such as by means of a radio frequency (RF) or induction heater 30 schematically illustrated in the drawing.

While component B is being heated and volatilized within container 12 the temperature of component A within container 11 is adjusted, desirably high enough to melt component A. Initially the temperature of component A within container 11 may be maintained less than the temperature of component B within container 12. As a result component B is vaporized from container 12 and contacts component A within container 11 and tends to condense thereon with the resulting formation of material AB. The vaporization and transport of vaporized component B to contact with component A and the resulting formation of material AB is continued with temperature adjustment of the material A within its container until the desired amount of material AB or composition of the melt has been formed within container 11. At this point the upper end of tube 10, e.g. about 10a or container 12, is cooler than the lower end of tube 10', e.g. container 11. Thereupon, motor 25 is operated to lower cage 22. Cage 22 is lowered until the lower end 15a of seed crystal holder 15 is positioned at about the level of the melt of material AB within container 11 such that seed crystal 16 of material AB is in contact therewith.

Upon contact with material AB Within container 11, material AB being maintained in the molten state therein by means of heater 30 crystal growth of material AB onto seeding material or seed crystal 16 takes place. During the crystal growing operation magnet 21 is slowly and continuously rotated, e.g. l0 r.p.m., about tube 10 thereby causing block 19 to rotate. Rotation of magnet 20 is effected by operating meter 35. As block 19 is rotated envelope 14 and seed crystal holder 15 are caused to rotate with it. At the same time or intermittently cage 22 is very slowly raised alongside of tube 10, causing energized solenoid 20 and cylinder 17 and envelope 14 and seed crystal holder 15 to move with it. When a sufficientlength of crystalline material AB has been grown upon seed crystal 16, the crystal growing operation is terminated and the resulting grown crystal removed from tube 10.

The above-described process for the manufacture of crystaline AB material provides a very flexible, versatile crystal growing operation as evidenced by the following possible modifications. Specifically, the crystal growing operation can be modified and/or controlled by varying the temperatures of portions of tube 10 and the materials A, B and AB therein. During the formation of AB the container containing A is always maintained at a temperature greater than that of container containing B. The temperature of B determines the vapor pressure of B in the system. As the vapor of B contacts A, AB is formed. If the container 11 is initially at a temperature such that the AB formed does not completely dissolve in the excess A, then the temperature has to be raised until all the AB has gone into solution. At that point the melt consists'either of equal proportions of A and B or has an excess of A or B depending on the pressure of B maintained in the system. Modification of material AB is affected by the temperature at which B is maintained at 12. The relative amounts of A and B do not matter as long as the amount of B is large enough to combine with A and to fill the vapor space to the desired pressure.

The following is illustrative of a practice of this invention. Cage 22 is lifted along the outside of and toward the upper end of tube 10 so as to move seed crystal holder out of container 11. Thereupon, an amount of gallium is introduced into container 11 and at least a stoichiometric amount of arsenic, preferably an excess, is introduced into container 12 and tube 10 evacuated to a pressure of about 0.0001 mm. Hg. Tube 10 is sealed and the components arranged therein as in the drawing.

Heat, by suitable means, is then applied to container 12 sufiicient to volatilize the arsenic therein while at the same time maintaining the temperature of the gallium within container 11 above the temperature of the arsenic within container 12, e.g. the arsenic within container 12 is maintained at a temperature in the range 500700 C. and the gallium in container 11 is maintained at a temperature in the range 600-1250 C. When the arsenic has been substantially completely vaporized from container 12 to contact and to react with the gallium in the container 11 with the resulting formation of gallium arsenide therein, the temperature of container 11 now containing gallium arsenide therein is adjusted to a temperature at least sufficient to melt the gallium arsenide therein, i.e. a few degrees, above about 1238 C., the melting point of gallium arsenide. During this operation the interior of tube 10 is filled with gaseous arsenic derivable from the arsenic supplied to container 12. Thereupon, cage 22 together with solenoid is lowered downwardly along the outside of tube 10 permitting seed crystal holder 15 to move downwardly within tube 10. Cage 22 is lowered until seed crystal 16, such as a seed crystal of gallium arsenide, carried at the end of seed crystal holder 15 comes into contact with the molten gallium arsenide within container 11. Magnet 21 is then slowly rotated about tube 10 and at the same time, either continuously or intermittently, cage 22 is very slowly raised along the outside of tube 10 so as to lift seed crystal holder 15 carrying with it seed crystal 16 and the resulting formed crystalline gallium arsenide thereon derived from the melt within container 11. After a sufiiciently large crystal of gallium arsenide has been thus formed, the crystal growing operation is terminated by lifting seed crystal holder 15 to withdraw the crystal gallium arsenide material suspended therefrom out of contact with the melt within container 11. The resulting formed crystalline gallium arsenide is then recovered as product.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made there in without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of producing, growing and pulling in a closed system a crystalline material having the composition AB which comprises maintaining a body of molten component A within a first container in a closed contacting zone, maintaining an amount of component B within a second container within said closed zone, heating component B to vaporize component B to bring component B into contact with component A within said zone under conditions such that component A reacts with component B to form composition AB within said first container, adjusting the temperature of said first container during the aforesaid contacting operation to a temperature to maintain the resulting formed composition AB dissolved in molten component A within said first container, continuing vaporizing and contacting component B with component A within said closed contacting zone until substantially all of said component B Within said Zone has reacted with said component A and forming a melt of resulting composition AB Within said first container, introducing seed crystal of composition AB into direct contact with said melt of composition AB within said first container within said closed contacting zone, maintaining said seed crystal of composition AB in contact with said melt of comopsition AB under crystal growing conditions to form crystalline material AB derived from said melt on said seed crystal and withdrawing from contact with said melt said seed crystal together with resulting formed crystalline material having the composition AB thereon.

2. A method in accordance with claim 1 wherein component A is gallium, component B is arsenic and wherein composition AB is gallium arsenide.

3. A method of producing, grow-ing and pulling in a closed system a crystalline material having the composition AB which comprises maintaining a body of molten component A Within a first container in a closed contacting zone, maintaining an amount of component B within a second container within said closed zone, heating component B to vaporize component B to bring component B into contact with component A within said zone'under conditions that component A reacts with component B to form composition AB within said first container, continuing vaporizing and contacting component B with component A within said closed contacting zone until substantially all of said component B within said zone has reacted with component A and forming a melt of composition AB within said first container, introducing seed crystals of composition AB into direct contact with said melt of composition AB within said first container within said closed contacting zone, maintaining said seed crystal of composition AB in contact with said melt of compsition AB under crystal growing conditions to form crystalline material AB derived from said melt on said seed crystal and withdrawing from contact with said melt said seed crystal together with the resulting formed crystalline material having the composition AB thereon.

References Cited UNITED STATES PATENTS 2,862,787 12./1958 Seguin et al. 24-14 2,979,386 4/ 1961 Shockley et al. 23-273 2,980,500 4/1961 Miller 2350 3,154,384 10/1964- Jones 148-1.6

OSCAR R. VERTIZ, Primary Examiner. MAURICE A. 'BRINDISI, Examiner. M. WEISSMAN, H. S. MILLER, Assistant Examiners. 

1. A METHOD OF PRODUCING, GROWING AND PULLING IN A CLOSED SYSTEM OF CRYSTALLINE MATERIAL HAVING THE COMPOSITION AB WHICH COMPRISES MAINTAINING A BODY OF MOLTEN COMPONENT A WITHIN A FIRST CONTAINER IN A CLOSED CONTACTING ZONE, MAINTAINING AN AMOUNT OF COMPONENT B WITHIN A SECOND CONTAINER WITHIN SAID CLOSED ZONE, HEATING COMPONENT B TO VAPROIZE COMPONENT B TO BRING COMPONENT B INTO CONTACT WITH COMPONENT A WITHIN SAID ZONE UNDER CONDITIONS SUCH THAT COMPONENT A REACTS WITH COMPONENT B TO FORM COMPOSITION AB WITHIN SAID FIRST CONTAINER, ADJUSTING THE TEMPERATURE OF SAID FIRST CONTAINER DURING THE AFORESAID CONTACTING OPERATION TO A TEMPERATURE TO MAINTAIN THE RESULTING FORMED COMPOSITION AB DISSOLVED IN MOLTEN COMPONENT A WITHIN SAID FIRST CONTAINER, CONTINUING VAPORIZING AND CONTACTING COMPONENT B WITH COMPONENT A WITHIN SAID CLOSED CONTACTING ZONE UNTIL SUBSTANTIALLY ALL OF SAID COMPONENT B WITHIN SAID ZONE HAS REACTED WITH SAID COMPONENT A AND FORMING A MELT OF RESULTING COMPOSITION AB WITHIN SAID FIRST CONTAINER, INTRODUCING SEED CRYSTAL OF COMPOSITION AB INTO DIRECT CONTACT WITH SAID MELT OF COMPOSITION AB WITHIN SAID FIRST CON- 